1. Field of the Invention
The present invention relates to a display device having a display function using a light-emitting element and a read function using the light-emitting element and an imaging device. Further, the invention relates to a display device having display surfaces on both sides.
2. Description of the Related Art
In recent years, as for a display device, research and development of display devices using light-emitting elements typified by electroluminescent elements is pushed forward instead of liquid crystal displays. Such a display device is widely used by utilizing advantages such as high image quality and wide viewing angle due to light emitting properties, and thinness and light weight that are achieved since it does not require a backlight. Further, there is a display device having a display function and a read function provided by integrating light-emitting elements and imaging devices into the display device (for example, Reference 1: Japanese Patent Laid-Open No. 2002-176162).
Further, among electronic devices each comprising a display surface, use of portable terminals is increased in particular, and further more sophistication and a high added value are demanded. Accordingly, a portable terminal having a sub display surface as well as a main display surface has been developed.
As to an electronic device provided with a sub display surface as well as a main display surface, the volume occupied by a module including a backlight and the like and the volume occupied by a control IC for driving the module are not negligible. In particular, portable terminals offered lately are remarkably reduced in weight, thickness, and size and that is a trade off for the high added value.
Further, in a portable terminal having a sub display surface, display surfaces of both sides are back to back. Accordingly, only one display surface has been able to be seen exclusively in either case a cellular phone is opened or closed despite two display surfaces are provided. Further, in the case of an electronic device of a folding type, it must be opened from the folded position to see the display surface inside, and thus causing a considerable inconvenience.